Manufacture of artificial filamentary material



1961 D. w. GROOMBRIDGE ETAL 3,003,845

MANUFACTURE OF ARTIFICIAL FILAMENTARY MATERIAL Filed Aug. 21, 1957 FIG.|

FIG. 2

United States Patent 3,003,846 MANUFACTURE OF ARTIFICIAL FILAMENTARY MATERIAL Denis William Groombridge and Reginald Henry John Riley, Spondon, near Derby, England, and James Hague Pearson, Thur-so, Scotland, assignors to British Celauese Limited, a corporation of Great Britain Filed Aug. 21, 1957, Ser. No. 679,471 Claims priority, application Great Britain Aug. 23, 1956 9 Claims. (Cl. 18-54) This invention relates to the manufacture of artificial filamentary material by a wet spinning process.

In one method of making artificial filamentary material a solution of the filament-forming substance in a spinning solvent is extruded into a liquid coagulant which is miscible with the spinning solvent but is a non-solvent for the filament-forming substance. In the coagulant the filament-formiug substance solidifies and the filaments so formed become/hardened or set more or less rapidly. In order to increase their tenacity the filaments, before they can become completely hardened, and while they are still in contact with the coagulant, are stretched. It is however well known that while this stretching operation increases the tenacity of the filaments it also tends to decrease their extensibility, and it has not proved easy to obtain wet spun filamentary materials, especially of cellulose derivatives such as cellulose acetates, which have both a good extensibility and a good tenacity. It is an object of the present invention to provide a new wet spinning method, whereby filaments combining these two properties can be obtained.

According to the invention artificial filamentary material is made by a wet spinning process which comprises extruding a solution of a filament-forming substance in the form of filaments into a liquid coagulant having a degree of softening or swelling action on the filamentforming substance, and before the filaments have become completely hardened stretching them while they are in contact with a liquid which has a higher softening or swelling action on the filament-forming substance than has the coagulant. In the preferred form of the invention the coagulant is a solution of the spinning solvent in a non-solvent. for the filament-forming substance, and the filaments are stretched in contact with a similar solution of higher concentration or at a higher temperature or both.

The invention is of particular importance and value in connection with the production of cellulose triacetate filamentary material by spinning an acetic acid solution an acetone-soluble cellulose acetate by extruding an acetone solution of the cellulose acetate into aqueous acetone or aqueous diethylene glycol diacetate, and the production of polyacrylonitrile filamentary material by extruding a solution of polyacrylonitrile in cyclic ethylene glycol carbonate into an aqueous, solution of cyclic ethylene glycol carbonate.

While an acetic acid solution of cellulose triacetate to be spun in accordance with/the invention may be obtained by dissolving preformed cellulose .triacetate in acetic acid, it is a particular advantage of the invention that it can be applied to the production of filamentary materials directly from acetic acid solutions of the cellulose triacetate such as are obtained in the acetylation process itself without any intervening precipitation and ice re-solution. Methods of acetylating cellulose to obtain such solutions are well known. In an usual method, which is very suitable for obtaining solutions specifically for use in the process of the invention, the cellulose, preferably after an activating pretreatment, is acetylated with acetic anhydride in the presence of sulphuric acid as catalyst and of sufiicient acetic acid to dissolve the cellulose acetate formed. When the acetylation is com plete it is usually advisable to subject the resulting cellulose triacetate to some degree of hydrolysis in order to split off, so far as possible, combined sulphate groups derived from the sulphuric acid catalyst. This is done by adding to the solution more than sufficient water to destroy unreacted acetic anhydride, and allowing the resulting hydrolysis to proceed either at room temperature or at an elevated temperature. When room temperature or moderately elevated temperatures are used all the acetylation catalyst may be present throughout the hydrolysis operation, but when higher temperatures are to be used, it may be advisable to neutralise part or even all of the catalyst before the hydrolysis in order to reduce or avoid the degradation of the cellulose triacetate, i.e. the reduction in its average molecular weight (chain length), which might otherwise occur under the conditions employed. Examples of suitable neutralising agents are magnesium carbonate and acetate. In any event any catalyst remaining after the hydrolysis step should be neutralised, advantageously by adding somewhat more than the equivalent quantity of neutralising agent. Even if no specific hydrolysis step is employed, it is advisable at least to ensure that no acetic anhydride remains in the solution. The concentration of the solution should if necessary be adjusted, as by the addition of further acetic acid, until its viscosity is suitable for spinning.

The solution so obtained is preferably heated for some time to a temperature above 70 C. and preferably about -85 C. or higher, as described in the application of Groombridge et a1. 679,516, filed August 21, 1957. The time for which the solution is heated is atgleast equal to, and preferably considerably exceeds, a minimum useful period which may be taken as varying inversely with the temperature and being about 3 hours at 70 C. and 10 minutes at (1., being otherwise limited only by the proviso that it should not cause an unacceptable degree of hydrolysis or degradation of the cellulose triacetate. For example the solution may be heated to 80-85 C. for seven days or more, and (provided its water-content is below about 1% and especially below 0.85% by weight) to 100 C. for four days or more; if on the other hand it has a substantially higher watercontent, eg 1-3% and especially l.252%, while it can still be heated to 80-85 C. for seven days or more, at 100 C. six hours will usually be a safe maximum. It will of course be realised that these figures are subject to some variation, according to the initial acetyl value and viscosity (average molecular weight) of'the cellulose triacetate and the amount of hydrolysis or degradation that may be acceptable in any particular case.

In a preferred method of working the acetylation solution, after it has been neutralised, is heated to about 80-85 C. with stirring or other form of agitation, and is forwarded .at this temperature, as by gravity feed or pumping, to the main filters, the time taken for the heating and the passage of the solution to the filters preferably being 12 hours or more, e.g. 12-100 hours. Advantageously before it reaches the filters the solution is heated for a relatively short time, e.g. 10 minutes to 3 hours, to l00-118 C. or, if pressure equipment is available, to a temperature above the boiling point of acetic acid, e.g. up to C. This extra heating step is best accompanied by thorough stirring or some other method of subjecting the solution to a vigorous shearing action. Its duration must be limited as already described so that no unacceptable degree of hydrolysis or degradation of the cellulose triacetate occurs. From the main filters the solution is passed, preferably still at 8085 (3., to the spinning positions, though before being actually extruded it is preferably cooled, e.g. to a temperature below 35 C. and especially-between 25 and 33 C.

The concentration of the aqueous acetic acid coagulant into which the solution is extruded preferably does not exceed about 25% by weight in the vicinity of the spinning jet, taking into account acetic acid derived from the spinning solution. Advantageously it is between about 5% and 18%, and especially between about 12% and 18%. The coagulant is preferably at a temperature such that its swelling action on cellulose triacetate is not greater than, and advantageously near, that of an 18% acetic acid at 18 C.

The filaments maybe stretched by passing them successively round two rollers, the second of which runs at a somewhat higher peripheral speed than the first. Advantageously each roller may be provided with yarn guides or a skew idler or driven auxiliary roller, to enable the filaments to pass round it a number of times without risk'of the various laps coming into contact. Stretching devices of this general kind are well known and need not here be further described.

In one method of putting the invention into practice the spinning solution is extruded into a bath of coagulant .having an acetic acid concentration (including that derived from the spinning solution) between about 12% .and 18%, and the filaments formed remain submerged in the bath at least until they are sufiiciently set to be handled without damage, and preferably until they are in substantial equilibrium with the coagulant, i.e. until no more acetic acid diffuses from the filaments into the coagulant bath. The coagulant may be contained for example in a horizontal trough into which the spinning solution is extruded and through which the filaments are drawn more or less horizontally, or it may flow through a tube which is mounted horizontally or vertically or at an angle to the vertical and through which the filaments also travel. After leaving the bath the filaments are led to the stretching rollers or other stretching device, for example by means of a godet.

The stretching device is arranged so that the filaments are subjected to the stretching tension while they are in contact with and softened by an aqueous solution of acetic acid of higher concentration or at a higher temperature or both than the coagulant. For instance one .or both stretching rollers may dip into or'besubmerged in such .a solution. For example the filaments may be stretched while softened by means of aqueous acetic acid of concentration about 35-65% at or near room temperature, i.e. about .15-25 C., or, as may often be more convenient, by means of acetic acid of concentration about 16-20% (i.e. about the same as that of the coagulant bath) at about 70-90 C., or intermediate concentrations and temperatures can be used. If desired filaments which are still wet with coagulant may be stretched while simply heated to a suitable temperature.

Another method of carrying out the invention, which is of particular value from the point of view of simplicity and economy, consists in extruding the spinning solution into a coagulant bath through which the filaments pass for a distance only sulficient, or not much more than sufiicient, to .give them coherance, and in any case much too small to allow them to attain equilibrium with the coagulant as regards acetic acid content. In many cases it is sufficient to pass the filaments through the bath for about 1-4 inches, though immersion over somewhat longer distances,e.g. 4-8 inches, may be necessary when spinning coarse filaments or when spinning at particularly high speeds. If the vessel containing the coagulant is made very "small, -e.g. .with a cross-sectional area little larger than is needed to contain the spinning jet, it is possible to supply the coagulant in the form of water or a highly dilute acetic acid, .for example such as results from the washing of the stretched filaments, the acetic acid needed to give the desired concentration being then derived wholly .or in part from the spinning solution. The filaments on leaving the bath are allowed to carry with thema substantial amount of coagulant, by means of which they become set to a greater extent as they travel through the air. This involves the transfer of acetic acid from the filaments to the liquid carried along by them, which thus becomes increasingly concentrated. It is ad- Vantageous to allow the process to continue until an approximate equilibrium as regards acetic acid content is established between the filaments and the liquid. The concentration of acetic acid at which this equilibrium is established can be readily controlled by means of an adjustable wiping or equivalent device, e.g. an adjustable yarn guide or adjustable squeeze rolls, positioned near the point at which the filaments leave the coagulant bath, and adapted to wipeoff or squeeeze'out part of the-coagulant which the filaments carry with them from the bath, and if desired to return it to the vicinity of the spinning jet. This adjustable wiping or equivalent device is preferably set so that approximate equilibrium between the filaments and the liquid. is established at an acetic acid concentration between about 40% and 55%. When or shortly before this equilibrium has been established, the filaments are in a suitable condition for stretching in accordance with the invention, and may be passed to a stretching device as already described, except of course that no further aqueous acetic acid need be applied to them.

The invention is particularly useful in the manufacture of tows containing large numbers of individual filaments, e.g. 1000 filaments or more, such as are employed in the production of staple fibres. It may however also be applied with advantage to the manufacture of other types of filamentary material, for example yarns of low or moderate denier and also monofils, e.g. thick filaments useful in making bristles and the like, artificial straw, etc., such materials being included within the term filaments as it is used in this specification.

The invention is illustrated by the following examples.

Example I A 12% solution of cellulose triacetate of acetyl value about 61% obtained by the acetylation of cellulose using sulphuric acid as catalyst in the usual way followed by a short hydrolysing operation, subsequent neutralisation of the catalyst by an excess of magnesium carbonate, and dilution, was heated to 70 -C. and stirred for 8 hours. It was then filtered and passed to a conventional spinning pump, which supplied it at a temperature of about 30 C. to a spinning jet containing 10,578 holes each of diameter 0.05 mm. arranged in segments separated by undrilled segments of the jet face. The coagulant bath consisted of aqueous acetic acid of concentration 16.9% and at a temperature of 18 C., contained in a horizontal trough about 3 feet long. After leaving the bath the filaments produced were led as a bundle or tow to a pair of stretching rollers dipping into a 19.4% aqueous acetic acid solution at a temperature of C. and set to give a 10% stretch. The resulting tow after 'being washed and dried had a denier of 44,100, a tenacity of 1.09 grams per denier and an extensibility of 18.7%. A product having similar properties could be obtained by stretching the tow in acetic acidof concentration 45% at a temperature of 23 C.

Example II The same spinning solution was extruded through an upwardly facing spinning jetcontaining 1528 holes each 0.05 mm. in diameter into a vessel just large enough to accommodate the ;jet fitting and extending about 3 inches above the jet face. An adjustable yarn guide was positioned above the vessel. Water was fed to the vessel at a rate suflicient to keep the vessel substantially filled with liquid without actually overflowing, i.e. at the same rate as liquid was carried away from the vessel by the filaments being formed. After leaving the vessel the filaments travelled as a bundle or tow for a distance of about 12 inches through the air to a pair of stretching rollers set to give a 16% stretch. The concentration of acetic acid in the vessel (derived from the water feed and the acetic acid from the spinning solution) was 17%, and the concentration of the acetic acid on the tow when it reached the stretching rollers was 47%. The stretched tow after being washed and dried had a denier of 8500, a tenacity of 1.02 grams per denier and an extensibility of 22.5%.

Example III A cellulose triacetate of acetyl value 61.07% was ob tained by acetylating cotton linters using acetic acid as the acetylation medium and sulphuric acid .as catalyst in the usual way and ripening for a short time. The catalyst was then neutralised, the cellulose triacetate con centration of the solution adjusted to 12.5% and water.

added to give a total water-content of 1.75%.

The solution was then heated for about 30 hour'sfto 80-85 C. in a circulating system, after which it passed to the main filters, After being filtered it was II, except that the yarn produced was stretched by-l8%. The product had a tenacity of about 1.3 grams per denier and an extensibility of about 30%. v I

Example IV The process of Example I was still at the same temperature. spun as described in Exampl repeated, except that and the tow was stretched in acetic acid at 65 C.

(a) by 12% and (b) by 50%. After being washed and dried the products had respectively tenacities of 1.27 and 1.89 grams per denier, and extensibilities of 28.7% and 16.0%. Similar products could be obtained from this spinning solution and these stretch ratios and conditions using the general method described in Example II. v

It was noted that products obtained by the method of working illustrated by Examples II and II usually had a higher lustre than those obtained by the method illustrated in Example I.

Apparatus which may be used for carrying out the invention is illustrated diagrammatically in the accompanying drawing, in which FIGURE 1 is a side view partly in section of a device suitable for carrying out a process such as is described in Example I, and

FIGURE 2 is a side view partly in section of a device suitable for carrying out a process such as is described in Examples II and HI.

Referring now to the drawing, the apparatus illustrated in FIGURE 1 comprises a trough 11 provided with an inlet 12 and outlet 13 for coagulant. A spinning jet 14, carried on a feed pipe 15, is mounted near the bottom of the trough 11 at the end at which the coagulant enters, and a yarn guide 16 is fixed at its other end at about the operating level of the surface of the coagulant. A godet 17 is mounted at a higher level.

A second trough 18 is provided for the stretch-assisting agent. Stretching rollers 19, 20 are provided towards the two ends of the trough 18, each having a skew idler roller 21, 22 respectively above it. The stretching rollers 19, 20 are driven at the desired speeds by conventional driving means (not shown).

In operation a spinning solution is extruded through the spinning jet 14 into the coagulant in the trough 11, and the yarn or tow 23 produced is drawn through and out of the coagulant round the yarn guide 16 by means of the godet 17. It then makes a number of laps round the roller 19 and its associated idler roller 21, passes through the stretch-assisting agent in the trough 18, and makes a number of laps round the roller 20 and its associated idler roller 22. The roller 20 is driven at a higher peripheral speed than the roller 19, the ratio be tween them corresponding to the amount by which the yarn or tow is to be stretched. From the roller 20 the yarn or tow passes to a washer and a drier of any suitable design (not shown).

The apparatus illustrated in FIGURE 2 comprises a spinning section 31 and a stretching section 32. The spinn'ing section comprises a small vertical spinning vessel 33 provided at the bottom with. an inlet 34 for liquid. A spinning jet 35 fed by a pipe 36 is mounted face upwards near the bottom of the vessel. A friction member 37 above the vessel 33 is adjustably mounted in such a way that the quantity of liquid which it wipes off from a yarn or tow 38 leaving the vessel and passing in contact with it can be varied at will. A godet 39 is positioned above the friction member 37.

, The stretching section 32 is similar to that illustrated in FIGURE 1, except of course that as the stretch-assisting agent is already on the yarn or tow 38 the trough 18 is not required; apart from this its several parts are identified by the same reference numbers as in FIGURE 1.

In operation the spinning vessel 33 is filled with water, and the spinning solution extruded into it through the spinning'ijet35 The filaments formed are drawn out of the spinning "vessel 33 by means of the godet 39, forming the yarn or tow 38, and making contact lightly with the friction member 37, the position of which is so adjusted as to leave on the yarn or tow the desired amount of liquid. From the godet the yarn or tow passes to the stretching section 32, where it passes in turn round the two stretching rollers with their associated idler rollers as in the device of FIGURE 1.

It is not necessary that the vessel 33 should be vertical or that the jet should face vertically upwards. It is however desirable that the axes of the vessel and the spinning jet should be at an angle of at least 45 to the horizontal, and the vertical position has proved to be of advantage.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the manufacture of artificial filamentary material, which comprises extruding an acetic acid solu tion of cellulose triacetate into a coagulating bath of aqueous acetic acid having an acetic acid concentration of about 5 to 25% by weight, withdrawing the resulting filaments from the coagulating bath before they have attained equilibrium with the bath, passing the filaments through air until theliquid from. the coagulating bath carried on the surfaces of the filaments has been considerably enriched with acetic acid by diffusion of the latter from the interior of the filaments, and stretching the filaments in air while carrying the acid-enriched liquid, the overall acetic acid concentration of the total liquid associated with the cellulose triacetate in said filaments at the time of said stretching being 40 to 55% by weight.

2. Process according to claim 1, wherein the length of passage of the filaments through the coagulating bath is from about 1 to 4 inches.

3. Process according to claim 1, wherein the temperature of the coagulating bath is such that it has a swelling action on cellulose triacetate not greater than that of 18% aqueous acetic acid at 18 C.

4. Process for the manufacture of artificial filamentary material, which comprises extruding an acetic acid solution of cellulose triacetate into a coagulating bath of aqueous acetic acid of from about 5 to 25 concentration, withdrawing the resulting filaments from the coagulating bath before they have attained equilibrium with the bath along with sufiicient coagulant so that the overall concentration of acetic acid in the total liquid associated with the cellulose triacetate in said filaments is about 40 to 55%, passing the filaments through air until the liquid from the coagulating bath carried on the surfaces of the filaments has reached equilibrium with the liquid in the interior of the filaments, and stretching the filaments in air while carrying the equilibrium liquid.

5. Process according to claim 4, wherein the temperature of the coagulating bath is such that it has a swelling action on cellulose triacetate approximately equal to that of 18% aqueous acetic acid at 18 C.

6. Process for the manufacture of artificial filamentary material, which comprises extruding an acetic acid solution of cellulose triacetate into a coagulating bath at about 18 C. and consisting of aqueous acetic acid of about 17% strength, withdrawing the resulting filaments from the coagulating bath after a passage therein of about 3 inches, passing the filaments through air over a distance of about 12 inches whereby the acetic acid content of the liquid carried on the surfaces of the filaments is raised to about 47%, immediately stretching them in air by about 16%, and thereafter washing and drying them.

7. Process for the manufacture of artificial filamentary material which comprises extruding a solution of cellulose triacetate in a solvent into a coagulating bath containing the components of said solvent, withdrawing from said bath filaments carrying on their surfaces a substantial amount of liquid of said coagulating bath, the period of contact between said bath and said extruded solution being sufiicient to form coherent filaments but being such that the solvent content of the interior of said filaments is considerably greater than the solvent content of said liquid on said surfaces, passing the filaments through air until the concentration gradient of the liquid associated with the cellulose triacetate throughout the crosssection of the filaments has been considerably reduced due to diffiusion of liquid between the interior and exterior of the filaments, and then stretching the filaments while carrying said liquid of reduced concentration gradient.

8. Process according to claim 7 wherein the duration of passage through air prior to stretching is suflicient for the liquid associated with the cellulose triacetate of said filaments to be in substantial equilibrium throughout the cross-section of the filaments.

9. Process according to claim 7 wherein said solvent is acetic acid and the liquid of said coagulating bath is dilute aqueous acetic acid.

References Cited in the file of this patent UruTED STATES PATENTS 16;;Alles Ian. 18, 1944 i .1 Johnson et a1. Nov. 3, 1953 a Tachikawa Ian. 24, 1956 -Wicker Mar. 6, 1956 Clouzeau Apr. 24, 1956 Taylor et 2.1. ....i.... Aug. 14, 1956 Pedlow 25, 1956 

1. PROCESS FOR THE MANUFACTURE OF ARTIFICIAL FILAMENTARY MATERIAL, WHICH COMPRISES EXTRUDING AN ACETIC ACID SOLUTION OF CELLULOSE TRIACETATE INTO A COAGULATING BATH OF AQUEOUS ACETIC ACID HAVING AN ACETIC ACID CONCENTRATION OF ABOUT 5 TO 25% BY WEIGHT, WITHDRAWING THE RESULTING FILAMENTS FROM THE COAGULATING BATH BEFORE THEY HAVE ATTAINED EQUILIBRIUM WITH THE BATH, PASSING THE FILAMENTS THROUGH AIR UNTIL THE LIQUID FROM THE COAGULATING BATH CARRIED ON THE SURFACES OF THE FILAMENTS HAS BEEN CONSIDERABLY ENRICHED WITH ACETIC ACID BY DIFFUSION OF THE LATTER FROM THE INTERIOR OF THE FILAMENTS, AND STRETCHING THE FILAMENTS IN AIR WHILE CARRYING THE ACID-ENRICHED LIQUID, THE OVERALL ACETIC ACID CONCENTRATION OF THE TOTAL LIQUID ASSOCIATED WITH THE CELLULOSE TRIACETATE IN SAID FILAMENTS AT THE TIME OF SAID STRETCHING BEING 40 TO 55% BY WEIGHT. 